Free space optical (fso) system

ABSTRACT

A detector configuration for use in a free space optical (FSO) node for transmitting and/or receiving optical signals has a plurality of sensors for detecting received optical signals. The plurality of sensors is configured along a common optical path and are used for separate functions. According, the detectors may be optimized for the respective function.

PRIORITY

This application claims priority to U.S. Application No. 62/208,561,filed Aug. 21, 2015, which is incorporated by reference in its entiretyinto this application.

BACKGROUND

In a two-node bi-directional Free Space Optical (FSO) communicationsystem, the two FSO nodes exchange data encoded on optical carrier beamssent across an unobstructed line of sight (LOS) between the two nodes.As shown in FIG. 1, a conventional two-node bi-directional system isillustrated. As shown, a first node 2 and a second node 3 communicate bytransmitting and receiving a signal 6, 7 sent between the nodes. Thedata can be encoded on the signals in any matter; a binary, on-off,exemplary signal is illustrated for simplicity. Each node has an opticaloutput 4 for transmitting the desired signal 6, 7, and also an opticalinput 5 for receiving the transmitted signal. Once received, theinternal electronics of the node can decode the signal and obtain thetransmitted data.

The communication system only works if the transmit path of the firstnode is aligned with the receiving components of the second node. Inorder to optimize tracking, conventional systems have split the receivedbeam into two paths: one for detection and one for alignment. As shownin FIG. 1, the exemplary system uses a beam splitter and separatedetectors as an alignment sensor and as a detector (processing) sensor.The resulting system is complex as it requires beam splitting andmultiple paths to perform each function (e.g. alignment and detecting).Errors are also introduced into the system through the misalignmentand/or drift between the multiple paths.

SUMMARY

A free space optical terminal is disclosed including a wave front sensorcomprising a free space in an interior region of the wave front sensor;and a receiver within the free space of the wave front sensor. Theresulting free space optical (FSO) terminal therefore may have a wavefront sensor used for aligning the system and a detector used to receivea data transmission received on an optical beam. In an exemplaryembodiment, the wave front sensor and the detector are different opticalcomponents, and the terminal may be configured such that a first portionof the received light is received at the wave front sensor and a secondportion of the received light source is received at the detector, wherea beam splitter is not used to separate the first portion from thesecond portion. Therefore, the first portion of light and the secondportion of light may follow the same optical beam path along an entirelength or along a portion of a length at the sensors within the system.In an exemplary embodiment, the first portion circumscribes the secondportion.

DRAWINGS

FIG. 1 illustrates and exemplary prior art free space optical system.

FIG. 2 illustrates an exemplary FSO node according to embodimentsdescribed herein.

FIG. 3 illustrates and exemplary front elevation view of a detectionsensor and alignment sensor described herein.

FIGS. 4-6 illustrate exemplary block diagram embodiments of FSO nodeshaving a common transmit and receive aperture—co-boresighted nodeaccording to embodiments described herein.

FIGS. 7A-7B illustrate exemplary system component configurationsaccording to embodiments described herein.

FIG. 8A illustrates an exemplary light alignment path on an exemplaryalignment sensor according to embodiments described herein. FIG. 8Billustrates an exemplary method of aligning a system according toembodiments described herein.

FIG. 9 illustrates a representative transfer function during analignment.

DESCRIPTION

The following detailed description illustrates by way of example, not byway of limitation, the principles of the invention. This descriptionwill clearly enable one skilled in the art to make and use theinvention, and describes several embodiments, adaptations, variations,alternatives and uses of the invention, including what is presentlybelieved to be the best mode of carrying out the invention. It should beunderstood that the drawings are diagrammatic and schematicrepresentations of exemplary embodiments of the invention, and are notlimiting of the present invention nor are they necessarily drawn toscale.

Exemplary embodiments may be used to greatly simplify the complexity ofa free space optical (FSO) terminal, while maintaining the benefitachieved by separate alignment and detection sensors. Accordingly,exemplary FSO terminals according to embodiments described hereininclude separate detection sensor(s) and alignment sensor(s) configuredor positioned such that the received optical path is maintained as asingle received optical path. Accordingly, exemplary embodiments mayreduce misalignment into the system by not subdividing the paths to theseparate detectors. An exemplary FSO terminal may be capable ofunidirectional or bi-directional high bandwidth optical communications.

Although embodiments of the invention may be described and illustratedherein in terms of an alignment sensor and detection sensor, it shouldbe understood that embodiments of this invention are not so limited, butare additionally applicable to functional components of the system. Forexample, the respective sensors may be used for other purposes.Accordingly, exemplary embodiments may be used when it is desired tohave two system components using portions of the same free space signaland it is desired to keep the components along the same signal path andnot split the signal into separate paths. Accordingly, the detector andalignment sensors described herein may be used for any system function.Moreover, exemplary embodiments may be adapted to other free spacesystems, not necessarily limited to optical applications orcommunication systems.

FIG. 2 illustrates an exemplary FSO node 10 according to embodimentsdescribed herein. The exemplary node 10 include transmit and receiveoptics as in conventional systems, which are not illustrated forpurposes of simplicity. However, as shown in the exploded portionillustrating the receive path, the detection sensor 12 is along the sameoptical path (receiving beam path 18) as the alignment sensor 14. In anexemplary embodiment, the alignment is achieved by incorporating a hole,aperture, or passage in the alignment sensor 14 such that a portion ofthe received beam falls on the alignment sensor and a portion of thereceive beam falls on the detection sensor 12.

As shown, the detection sensor is positioned out of plane from thealignment sensor. However, such configuration is not necessary. In anexemplary embodiment, the system includes a lens 16 or other optics fordirecting and/or focusing the received light 18 toward the sensor(s).The detection sensor 12 is shown positioned approximately at the focalpoint of the received path as set by lens 16. The alignment detector isshown positioned in a plane after the lens 16 and before the focal pointat the detection sensor 12, relative to the received optical path 18 (orbetween the focal point and the optics defining the focal point). Thedetection sensor 12 may be in plane with the alignment sensor 14, out ofplane with the alignment sensor 14, or before or after the alignmentsensor 14. The purpose of the sensors may also be swapped such thatsensor 14 is the detection sensor and detector 12 is the alignmentsensor. For example, the alignment sensor is a central sensor, while thedetection sensor is the annular sensor. Multiple annular sensors may beincorporated for different purposes to permit two or more detectorfunctions on the same optical path. The component shown as the detectionsensor 12 may also be any combination of optical components. Forexample, the detection sensor may be replaced with other components,such as mirrors, lenses, splitters, optical fibers, etc. that is used todirect the light before the detection sensor. Exemplary configurationsof such additional component combinations are described with respect toFIGS. 4-5.

FIG. 3 illustrates and exemplary front elevation view of the detectionsensor 12 and alignment sensor 14 having a common optical receive pathas seen elevated from a direction normal the detection surface. Asshown, the detection sensor 12 and alignment sensor 14 are concentric.In an exemplary embodiment, at least the outer perimeter of thealignment sensor 14 circumscribes and is positioned radially outside thedetection sensor 12 when viewed from a front profile. The alignmentsensor 14 may be longitudinally offset from the detection sensor 12along the optical receive path but still may radially circumscribe thedetection sensor when viewed in profile from a perspective of theoptical path (front face of the sensor(s)). FIG. 3 illustrates thedetection sensor 12 as being radially smaller than an inner diameter ofthe aperture of the alignment sensor 14. However, such a relationship isnot necessary. As shown in FIG. 2, the outer diameter of the detectionsensor 12 is greater than the inner diameter of the passage defined bythe alignment sensor 14.

FIG. 3 illustrates an incoming beam 18 offset on the alignment sensor14. As provided in FIG. 6, an exemplary method of aligning a system 60may use the coaxial alignment and detection sensors. At step 62, thealignment system and detection system are coaxially aligned. Thealignment system may be the quad-cell as described herein with respectto FIG. 3 or some other combination of optics/sensors to obtain asegmented detection of the incoming light. The detection system may bethe detection sensor as illustrated with respect to FIG. 3. However, thedetection system may also include other configurations such as those ofFIGS. 4-5 in which the light is further manipulated through otheroptics, such as splitter(s), len(s), optical fiber(s), mirror(s), andcombinations thereof before reaching the detection sensor. The coaxialarrangement permits the same receive optical path to be used with twodetection systems, where each detection system is used and can beoptimized for its own function (i.e. alignment/detection/other).

At step 64, the alignment sensor can detect the horizontal and verticaldisplacement of the beam 18 on the detector face. At step 66, thedisplacements may be determined or calculated based on a comparison ofthe detected signals from step 64. For example, the ratio of thedifference of the light on each half of the detector divided by thewhole by be used to determine a percentage offset from the center of thedetector in orthogonal (x-y) directions. In this case, the xdisplacement will be the signal difference from the total of the firstand second quadrants minus the total from of the third and fourthquadrants divided by the total signal: [(14 a+14 b)−(14 c+14 d)]/(14a+14 b+14 c+14 d). Similarly, the y displacement can be determined bycomparing the signal from the upper quadrants to that of the lowerquadrants [(14 a+14 d)−(14 b+14 c)]/(14 a+14 b+14 c+14 d). At step 68,the system may be manually or automatically adjusted to realign the nodesuch that the received beam 18 is centered on the detection sensor 14.After the system is aligned, at step 70, the detection sensor may beused to detect the incoming light, which is decoded by the system.

FIGS. 4 and 5 illustrate exemplary embodiments in which the transmit andreceive aperture of the node are the same—co-boresighted node. In thesecases, the transmit and receive paths are shared for at least a portionof the optical path traveled within the node. Ultimately, the transmitand receive paths will split, and FIGS. 4 and 5 illustrate differentconfigurations of when the split may occur.

FIGS. 4-6 are system block diagrams to illustrate exemplary features andalternatives within the scope of the present invention. For example,different combinations of optics are uses in different orders tointegrate and/or separate the optical path at different points. Thesystem components may be integrated, separated, rearranged, removed,duplicated, or other components added and remain within the scope of theinstant disclosure. FIGS. 4-6 illustrate a co-boresighted node in whichthe transmit and receive optical paths are aligned, co-axial, orconcentric for at least a portion of the optical path. As shown, the FSOnode comprises a common transmit and receive aperture.

FIG. 4 illustrates an exemplary co-boresighted FSO node having a commontransmit and receive optical path. As shown, the node 20 includes acommon transmit and receive path for outgoing and incoming opticalsignals. The system can include a co-boresighted beam steering unit 27that can align the beams with the internal optics. The common opticalpaths may then be split into the separate transmit and receive paths ata splitter or separator 25. This component can be any optical componentor beam splitter to separate the beam paths, such as a dichromic mirror,circulator, etc. Once separated, the transmit beam path comprises anoptical transmitter 23 to generate the optical signal according to theFSO Modem and processor. The received beam path comprises the opticsassociated with aligning and detecting the signal. The received optics26 may include any combination of optical components for directing,focusing, or otherwise manipulating the incoming beam for detection,processing, orienting, directing, filtering, or other function. Asshown, the received alignment sensor 24 passes at least a portion of thelight to the received detection sensor 22 such that these two sensorsare along the same beam path. The received alignment sensor 24 isconfigured as described herein. For example, the received alignmentsensor 24 may be any configuration of sensors to receive a portion ofthe received light from the outer periphery of the light beam, andpasses the portion of the light at the center of the beam. As describedherein the alignment sensor 24 and detection sensor 22 may beinterchanges, may be in the same focal plane, may be longitudinallydisplaced along the received beam path, or otherwise arranged asdescribed herein. The alignment sensor 24 communications with PATcontroller 21 to adjust the optics and beam steering in response to thedetected signal as described herein. The detection sensor 22communications with the FSO modem to analyze and decode the receivedoptical signals once converted to electrical form. The optical pathbetween any system components may be along a free space path, through anoptical component such as an optical fiber, or combinations thereof.

FIG. 5 illustrates an exemplary co-boresighted FSO node having a commontransmit and receive optical path. In this configuration, a largerportion of the common path is integrated so consolidated control andalignment. As shown, the beam steering platform 37 includes the transmitand receive optics for filtering, directing, focusing, etc. the beam inand out of the FSO node 30. A receive alignment sensor 34 is configuredto receive a portion of the received light and pass a portion of thereceived light. The passed, unobstructed light is then split at a beamsplitter 35 between the receive path to the received detector 32 and thetransmit source 33, each of which are coupled to the FSO modem forsignal processing and control. The PAT controller 31 controls the beamsteering unit 37 based on the detected signal from the alignment sensor34. This configuration may use free optical paths and/or guided opticalpaths, such as through a light guide or optical fiber. As shown, aterminal end of an optical fiber 38 is positioned at the focal point ofthe receive optics to direct the light through the system. The lightpath between box 38 and 35 or other components may be through an opticalfiber. As shown, an optical fiber may be positioned at or adjacent thefocal point of a focusing lens within the receive/transmit optics 36.The optical fiber may couple to two other optical fibers for directingthe light to and from the receive sensor 32 and transmit source 33. Thebeam splitter 35 or other optical components used herein may include acirculator, splitters, optical fibers, and other components as describedin U.S. Pat. No. 8,260,146 and U.S. Pat. No. 6,721,510, incorporated byreference in their entirety herein.

FIG. 6 illustrates an exemplary arrangement in which the alignmentsensor 44 is forward in the system optical path adjacent the nodeaperture. As shown, transmit and receive optics 46 may be used to focusor otherwise manipulate the light onto the alignment system 44 andthrough the rest of the system. After passing through the aperture ofthe alignment sensor, the light may be split at splitter 45 and focusedthrough more optics or otherwise directed through optical fibers 48 tothe detection sensor 42 and transmit source 43 respectively. The PATcontroller 41 may be used to control any combination of the Tx/Rx optics46 and/or the optical fibers 48 leading to RX detector 42 and/ortransmit optical source 43.

FIG. 7A illustrates a component representation of the block diagram ofFIG. 6 for illustrative purposes. As shown, the incoming beam 18 isfocused through optic 16 (Tx/Rx optics 46 of FIG. 6) that may be anyconfiguration or combination thereof described herein. A portion of thelight 18 a is focused on alignment sensor 14 RX alignment sensor 44 ofFIG. 6), while a portion is passed through aperture of alignment sensor14. Additional Tx/Rx optics 46 of FIG. 6 may include a series of lenses12 b and/or splitter 12 c to separate and focus the transmit and receivebeams on respective terminal ends of optical fibers 12 d. The PATcontroller 41 may be used to translate the optical fibers 12 d in one,two, or three dimensions to assist in system alignment.

Exemplary embodiments of the alignment sensor comprise a sensor portiondefining an outer section and an aperture through a central section. Thecentral section may be coaxial with the center of the optic or may beoff-center from the optic. The alignment sensor therefore includes acentral aperture 13 circumscribed by a plurality of sensors. In anexemplary embodiment, the central aperture is surrounded by two or moreand preferable three to six detectors. The detectors may circumscribethe aperture and substantially fill a perimeter around or substantiallysurround the aperture, where substantially can be understood by a personof skill in the art to include more than a majority and is approximatelythe entire perimeter but accounts for dead space between sensors andpositioning tolerances required between components. The detection sensor12 (either an outer perimeter or the working surface of the detectorarea) can be larger, smaller, or approximately equal to the aperture.The detection sensor 12 may be positioned in front of, flush with, orbehind the alignment sensor surface 14.

As seen in FIG. 3, an exemplary alignment sensor is a quadcell havingfour distinct detection areas 14 a-14 d. As shown, a quadcell detectormay be used as the plurality of detectors circumscribing the aperture.The quadcell includes a central hole positioned between the fourdetecting cells or quadrants. The hole is sized to permit the desiredbeam transmit/receive signal to align with the detection sensor or otheroptical components as described herien. The quadcell may be positionedsuch that the detection sensor axis (normal to the sensing face) isaligned with the center of the quadcell. The detection sensor may bepositioned at the center of the quadcell or may be positioned behind thequadcell (or on an opposing side than the inlet/outlet aperture of theterminal). Exemplary embodiments may also reposition the detectionsensor and use other optical components to direct the beam to thedetection sensor, such as an optical fiber. In which case, the terminalend of the optical fiber can be positioned in place of the detectionsensor as described herein.

FIG. 7B illustrates an exemplary configuration similar to FIG. 3 withthe inclusive of an internal baffle to isolate transmitted light fromthe alignment sensor for an FSO node having a common transmit/receiveaperture. Especially if the transmit and receive beams use the same orsimilar wavelengths, then the alignment sensor may detect backscatterfrom the transmitted wave and cause the system to realign based onauxiliary backscatter light instead of that received from the opposingFSO node. Accordingly, an internal baffle cone could serve to provideisolation between the transmit and receive beams if a similar wavelengthis used. As shown, a baffle 17 in incorporated in the optical path toseparate the received light 18 into two portions: the detected portion18 b and the alignment portion 18 a. The detected light 18 b is focusedonto a terminal end of an optical fiber 12 a configured to receive lightand direct the light to a detection sensor, and transmit lightoriginating from a light source. The alignment light portion is focusedor directed onto the alignment sensor 14. When the transmitted beam ispropagated from the optical fiber 12 a, the light is separated orisolated by the baffle 17 and does prevented from entering the alignmentportion 18 a.

For a bi-directional link between two FSO nodes, exemplary embodimentsmay be used such that the incoming data beam can also be used fortracking. In an exemplary embodiment, an exemplary free space opticalnode may include any combination of:

a common objective lens for transmit (Tx) and receive (Rx);an annular area around the Tx is captured by the quadcell with a holefor guiding; for a uni-directional link, the quadcell can be chosen tomatch the wavelength of the guide beacon, or use nearly the samewavelength as the Tx.for a bidirectional link, the Tx and Rx can be separated with a beamsplitter or optical circulator;for use with a Tx/Rx fiber, the quadcell and Tx/Rx fiber could beintegrated into a structure that eliminates the need for beamsplitters,simplifying the mechanical design; and/or an internal baffle cone couldserve to provide isolation between Tx and Rx if a similar wavelength isused.

The above features are exemplary only, and may be used in anycombination or sub-combination as is desired for the application. Otherfeatures may be added or the above features may also be modified toachieve the objective of a user. For example, ranges, such as forwavelengths, may be redefined for particular applications, distances,environments, etc. Also, features may be removed and others redefined toaccommodate the removal of a feature, such as the added or removedbaffle cone of exemplary FIG. 7B above.

Exemplary embodiments may be used to align and use (send/receivesignals) the terminal while reducing system complexity. Exemplaryembodiments use an increased lens size and use the light with a highernumerical aperture (NA) on a wave front sensor (WFS), such as a quadcellwith a hole. An annular ring from this section of the objective will beseen on the quadcell. The inside annulus comes from the hole in the quadwhile the outside comes from the edges of the objective. Any angularchange moves this outside edge shifting the balance of light on thequadrants.

Part of the tuning parameters of the system include the position of theoptics, such as the sensors and/or optical fibers (see, e.g. FIG. 7A).For example, a position of the alignment wave front sensor inside afocal plane of the corresponding light on the detection sensor changesthe hole size, and also allows changing the field of view (FOV) andlinear region over which it works. In practice, linearity only reallymatters when the beam is centered and the link is in operation. Duringacquisition with large angle errors, knowing the sign is enough to steertowards the center.

In an exemplary embodiment, the detection sensor and alignment sensormay be along an optical path, but used with different optical beams.Specifically, if the two sensors detect different wavelengths andtransparent to the wavelength of the other sensor, then the backscatteror other interference between the sensors is reduced or eliminated.However, two light sources are necessary at the sending node to bereceived. For example, if an FSO system is using 1550 nm wavelengthlight for transmitting data (the detection sensor), a silicon quadcellcould be used as an alignment sensor as it is transparent at the datawavelength. In this embodiment, a guide beacon would be chosen forSilicon and the data transmitted on 1550 nm. Therefore, an extremelyhigh isolation can be achieved without the baffle cone.

FIG. 8A illustrates an exemplary light alignment on an exemplaryquadcell as the beam is positioned. The receive beam is seen on thequadcell. The upper quadrants detect more light and therefore, theterminal can be moved upwards, or the transmitting beam (other terminal)moved downwards. The beam can be aligned such that it is centered on thequadcell and therefor on the centered optical fiber within the apertureof the quadcell. A representative transfer function is illustrated inFIG. 9. This one is notional for a particular application, but shows thebasic behavior.

Exemplary embodiments described herein include using a free spaceoptical terminal in which a portion of the received beam is used foraligning the system and a separate portion of the beam is used forreceiving, transmitting, and any combination thereof for a data signal.The exemplary method can be used without a beam splitter that separatesthe beam into separate paths. In an exemplary embodiment, the firstportion of the beam used for alignment is an exterior portioncircumscribing the second portion used for transmitting and/or receivingthe data signal. Therefore, the first portion may be a central portion,while the second portion may be a circumferential exterior portion ofthe same beam. Exemplary embodiments may also capture the entire beamfor communication by positioning the detection sensor before thealignment sensor and focusing the light on the detection sensor. Inexemplary embodiments, a controller is coupled to one or more opticalcomponents to adjust or control the position of the components and areable to position, aligned, or alter the working components of thesystem.

The method may include receiving an optical beam at the FSO terminal.The method includes positioning the beam such that a first portion fallson one or more detector(s) for aligning the terminal with the receivedbeam (or any first system function), and a second portion falls on oneor more receiver(s), such as a fiber optic or detection sensor, fordetecting and/or directing the signal for analyzing a data signalcarried on the received light. The system is configured such that thedetector(s) circumferentially surround the receiver(s).

As shown and described, a quadcell is used to illustrate the pluralityof detectors around the optical fiber or detection sensor. However, itshould be understood that any combination of detectors may be positionedaround the common receive/transmit path. The detectors may be of thesame kind, or may be different. There are variants for the tilt sensorchoice and a quadcell is not exclusive. Anything from normal quads tocustom multi pixel detectors including focal plane arrays with randomsub array read out may be used. Exemplary embodiments permit the lightto pass through a hole, aperture, or space between detectors, or have amaterial that transmits the light used for data transmission.

As shown and described, the receiver for receiving and transmitting thelight for data transmission is shown and described interior thedetectors for alignment or other system function, such that thedetectors circumferentially surround the receiver. However, thesefunctions and/or components may be switched and is not limited to theexemplary embodiment described.

“Substantially fill” or “substantial” is intended to mean greater than amajority, such as more than 75%. A majority is intended to mean 50%.Numerical ranges are also used herein and are approximations only.Approximations are understood to be within the person of skill in theart. For example, when a series of detectors approximately fullysurround or circumscribe an optical fiber, it is understood that naturaldead space or gaps must accompany the areas between the detectors. Theseapproximations are within the skill of the art to determine and maydepend on system components, tolerances, wavelengths, system size, etc.Therefore, approximately fully surround is understood to have detectorspositioned around the detectors to minimize the dead space, but would bedependent upon the kind and quantity of detectors selected. An opticalbeam path is understood to be the linear longitudinal direction of apropagated beam.

Exemplary embodiments may be incorporated into a free space opticalterminal used for both transmitting and receiving data signals. In anexemplary embodiment, the FSO terminal may use common optics fortransmitting and receiving a data signal therefrom/thereto. For example,U.S. application Ser. No. 14/608,166, titled “Data Retransmission forAtmospheric Free Space Optical Communication System,” owned by thepresent applicant, and incorporated by reference in its entirety herein,discloses an FSO unit that may use a common aperture and optics fortransmitting and receiving a data signal. Exemplary embodimentsdescribed herein may be used in conjunction with or replace thecomponents for alignment and detecting. For example, the componentslabeled 20, 22, and 24 of FIG. 2 of the Data Retransmission applicationmay be replaced by embodiments described herein. Other exemplary systemsthat may inform alternative configurations of the instant inventioninclude, but are not limited to those disclosed by U.S. application Ser.No. 14/608,133, filed Jan. 28, 2015, titled “Free Space OpticalCommunication Tracking with Electronic Boresight Compensation . . . ”,U.S. Provisional Application No. 62/238,637, filed Oct. 7, 2015, titled“Fast Tracking Free Space Optical Module,” and U.S. ProvisionalApplication 62/266,710, filed Dec. 14, 2015, titled “Free Space OpticalSystem with Common Transmit and Receive Paths,” both filed concurrentlyherewith, and incorporated in their entirety herein.

Although embodiments of this invention have been fully described withreference to the accompanying drawings, it is to be noted that variouschanges and modifications will become apparent to those skilled in theart. Such changes and modifications are to be understood as beingincluded within the scope of embodiments of this invention as defined bythe appended claims.

The invention claimed is:
 1. A free space optical terminal, comprising:a wave front sensor comprising a free space in an interior region of thewave front sensor; a receiver concentric with the free space of the wavefront sensor.
 2. The free space optical terminal of claim 1, wherein thereceiver comprises an optical fiber.
 3. The free space optical terminalof claim 2, wherein the optical fiber is a bi-directional fiber.
 4. Thefree space optical terminal of claim 2, wherein the optical fiber is auni-directional fiber.
 5. The free space optical terminal of claim 1,wherein the wave front sensor is a plurality of sensors circumscribing aperimeter of the receiver as seen from a front view normal to areceiving surface of the receiver.
 6. The free space optical terminal ofclaim 5, wherein the plurality of sensors substantially completes aperimeter around the receiver as seen from the front view.
 7. The freespace optical terminal of claim 6, wherein the plurality of sensorsapproximately completely completes the perimeter around the receiver asseen from the front view.
 8. The free space optical terminal of claim 5,wherein a terminal surface of the optical fiber is positioned in planewith a working surface of the plurality of sensors as oriented withrespect to an incoming received beam.
 9. The free space optical terminalof claim 5, wherein the plurality of sensors comprises a quadcell. 10.The free space optical terminal of claim 9, wherein the free space isdefined by a hole in the center of the quadcell.
 11. A free spaceoptical (FSO) terminal, comprising: a wave front sensor used foraligning the system and a detector used to receive a data transmissionreceived on an optical beam, wherein the wave front sensor and thedetector are different optical components, the system being configuredsuch that a first portion of the received light is received at the wavefront sensor and a second portion of the received light source isreceived at the detector, where a beam splitter is not used to separatethe first portion from the second portion.
 12. The free space opticalterminal of claim 11, wherein the FSO terminal is configured to transmitand receive with common optics.
 13. The free space optical terminal ofclaim 11, wherein the first portion and second portion follow the sameoptical beam path along an entire length within the system.
 14. The freespace optical terminal of claim 12, wherein the first portioncircumscribes the second portion.